Periodontal disease in the main cause of tooth loss in persons over age 40. While the disease has been shown to be of microbial etiology, the role of specific microorganisms has yet to be determined. One qroup of bacteria, the treponemes, has been traditionally and consistently associated with periodontitis, but due to technical problems with culturing a true relationship has not been established. The purpose of this study is to increase understanding and define the ecology of oral spirochetes. The specific aims of this research are to: 1) develop a specific and rapid identification system based on nucleic acid sequences, 2) develop a sensitive detection system utilizing the polymerase chain reaction (PCR), 3) use conserved 16s like ribosomal RNA sequences and cloning to sequence, characterize, and develop probes for treponemes that have resisted culturing, and 4) to use fluorescent DAN sequencing technology to quantitate relative proportions of each species of spirochete in the population. The ability to generate precise information on the composition of the spirochetal flora associated with periodontal health status should significantly increase understanding of this host-parasite interaction with the ultimate goal providing early diagnostic information.